Field of the Invention and Description of the Prior Art
Numerous systems have been proposed for treating water to provide an odor and taste-free product. Active chlorine-based inorganic and organic compounds supplied in both solution and solids forms, have been used for many years. These compounds, when mixed with water, generate the disinfectant hypochlorous acid which imparts a distinct taste and odor to the water. Hypochlorous acid is in chemical equilibrium with the hypochlorite anion (pKa=7.5).
In the book entitled Inhibition and Destruction of the Microbial Cell, W. B. Hugo, editor, 1971, J. R. Trueman points out in Chapter 3E (The Halogens):
"Sodium hypochlorite is a sterilizing agent in that it will kill all forms of microorganism. The spectrum includes viruses, non-acid-fast vegetative bacteria, acid-fast bacilli, bacterial spores, fungi, algae and protozoa. The most resistant forms of microbial life are bacterial spores, so that the ultimate criterion of a sterilizing agent is sporicidal activity. The view has been expressed that no chemical disinfectant is available which will kill bacterial spores (Gibson, 1968). On the other hand there is a wealth of information available to substantiate the fact that sodium hypochlorite is sporicidal (Finch, 1958)(p. 150)."
Chemical treatments typically follow a first purification step wherein the water is filtered to remove organic material and other suspended particulates. Generally, between 1 and 200 parts per million (ppm) of active chlorine (as hypochlorite) are then utilized to disinfect water, depending upon the level of reactive organic material present in the water and the type of suspected pathogens which must be eliminated. Often, between 1 and 10 ppm is added to food processing plant process water, while food handling equipment and surface-contaminated meat and fish may be routinely disinfected with 100 to 200 ppm chlorine. By contrast, the chlorine level typically found in public drinking water is seldom greater than 1 ppm.
Significant drawbacks associated with the utilization of high levels of chlorine to disinfect microbially contaminated water include the disagreeable taste and the odor of hypochlorous acid and hypochlorite (hereinafter referred to collectively as "hypochlorite"). Several systems are disclosed wherein chlorine-type treatments are used after hydrogen peroxide treatment. For example, in U.S. Pat. No. 4,243,525 issued Jan. 6, 1981 to Greenberg for "Method For Reducing The Formation of Trihalomethanes In Drinking Water", trihalomethanes are reduced by adding hydrogen peroxide to the water prior to chlorination. In the most preferred embodiments, the water is treated with 0.1 to about 50 ppm of hydrogen peroxide, following which sufficient chlorine is reacted with the hydrogen peroxide to maintain a residual amount of chlorine sufficient to disinfect the water and reduce the formation of trihalomethanes to less than 295 parts per billion (ppb).
In U.S. Pat. No. 4,693,832 issued Sep. 15, 1987 to Hurst for "Preparation Of Safe Drinking Water" the disinfection process comprises a first semi-finishing step and then adding dilute solutions of hypochlorous acid having a pH between 3 and about 6. Among the various pre-treatment steps referred to are treatments with chlorine dioxide, chlorine, hypochlorous acid, ozone, hydrogen peroxide and potassium permanganate.
Other water treatment systems are described in U.S. Pat. No. 2,105,835 issued Jan. 18, 1938 to Krause and entitled "Sterilizing Liquid"; U. S. Pat. No. 2,512,566 issued Jun. 20, 1950 to Marks, et al. for "Method of Sterilizing Small Quantities Of Water"; U.S. Pat. No. 4,239,622 issued Dec. 16, 1980 to Ridgway for "Process For The Disinfection Of Water"; and U.S. Pat. No. 4,367,149 issued Jan. 4, 1983 to Kinman for "Water Purification Process". A commercial product known as Potable Aqua.RTM. uses a two step approach employing an iodine tablet and a subsequent ascorbic acid tablet for neutralization.
What is missing from the teachings of the prior art covering hypochlorite-based disinfection of drinking water is a final drinking water product which is odor and taste-free and which preferably contains neither hypochlorite residues nor organic chemical carrier residues typically associated with hypochlorite generating tablets (e.g. Halazone and dichloroisocyanurate). In addition, organic hypochlorite generating tablet systems which are based upon first dissolving the tablet and subsequently hydrolyzing the dissolved organic compound to generate hypochlorite are slow and inconvenient. A treatment system which would overcome the aforementioned disadvantages of the prior systems would represent a significant advance in this technology.